Isatin derivatives were condensedby refluxing ethanol with thiazolobenzimidazole, yielding four linked 2-oxoindolin-3-ylidene)benzo [4,5]imidazo-[2,1-b]thiazol-3(2H)-ones. Thermal evaporation was used to deposit thin films of the produced 2-oxoindolin-3-ylidene)benzo [4,5]imidazo-[2,1-b]thiazol-3(2H)-one derivatives, which underwent thorough analysis employing UV–Vis and NIR spectroscopy. The spectral profiles of these materials were scrutinized with respect to their absorption, dielectricconstants, and dispersion propertiesand compared to previously published data. The current samples were suitable for application in optoelectronic devices, particularly as solar-absorbent materials, due to their high absorption coefficient (α > 10⁵cm⁻¹) at a solar maximum wavelength (λ = 500 nm). Additionally, their band and optical gap energies have been determined as 3.60, 3.56, 2.53, and 3.24 eV. The conclusions drawn from geometry optimization and nonlinear optical (NLO) calculations, performed using density functional theory (DFT) with the Becke, 3-parameter, Lee–Yang–Parr (B3LYP) approach at the 6–311G (d,p) level, further support these findings.